Waiman Long [off-list ref] wrote:

That is not as simple as I thought. First of that, there is not an
equivalent kzvfree() helper to clear the buffer first before clearing.
Of course, I can do that manually.

Yeah, the actual substance of vfree() may get deferred.  It may be worth
adding a kvzfree() that switches between kzfree() and memset(),vfree().

With patch 2, the allocated buffer length will be max(1024, keylen). The
security code uses kmalloc() for allocation. If we use kvalloc() here,
perhaps we should also use that for allocation that can be potentially
large like that in big_key. What do you think?

Not for big_key: if it's larger than BIG_KEY_FILE_THRESHOLD (~1KiB) it gets
written encrypted into shmem so that it can be swapped out to disk when not in
use.

However, other cases, sure - just be aware that on a 32-bit system,
vmalloc/vmap space is a strictly limited resource.

David